This invention pertains to a process for bonding lubricant to a magnetic disk and more particularly, to a process for bonding lubricant to a magnetic disk of a hard disk drive in order to decrease the flying stiction during the operation of the hard disk drive.
Hard disk drives generally use magnetic head assembly which contains air bearing sliders to read/write data on the surfaces of magnetic disks. Magnetic head assembly is supported and moved by actuator arms for positioning. In addition the slider of the hard disk drive contains read/write transducers for data acquisition and storage. Generally, magnetic disks have two discrete zones. A "landing zone" (or "CSS zone" abbreviated from "Contact Start Stop zone") is the zone where the slider rests while the hard disk drive is off, and takes off when the hard disk drive is started up. A "data zone" is the zone where the slider flies and reads/stores data by using the read/write head. The landing zone usually locates in the inner diameter of the magnetic disk.
When the power of a hard disk drive is turned on, enough force has to be applied for the slider to overcome the static friction or "stiction" force on the slider. During takeoff and landing, the slider maintains almost constant contact with the magnetic disk. Lubricant over the landing zone is important for decreasing wear and drag force during takeoff and landing. The CSS test method is commonly used for the stiction/wear durability measurement. This stiction is measured by repeating takeoff and landing of the magnetic head assembly until wear of the disk surface is induced. The measured data of static stiction is an important factor to predict the lifetime of a hard disk drive.
As the speed of the magnetic disk increases, the air in contact with the surface of the magnetic disk lifts the slider away from the surface. During the read/write (R/W) operation of the hard disk drive, the magnetic head assembly is moved by the actuator arm to fly over the data zone without contacting the magnetic disk. However, the magnetic head assembly occasionally contacts the disk during R/W operation. Most of these in-flight contacts are caused by collision of the slider with media asperity, corrosion products or other contaminant particles. Lubricant on the data zone minimizes wear and damage to the disk due to these in-flight contacts, but increases the flying stiction between the magnetic head assembly and the disk surface. In addition, in order to prevent damage caused by contacts, a protective overcoat of diamond-like carbon is sputtered on the magnetic disk about 200 Angstroms thick. A lubricant layer is then formed upon the overcoat layer about 20 Angstroms thick. In general, the lubricant layer includes a bonded lubricant layer bonding to the overcoat layer and a free lubricant layer upon the bonded lubricant layer. The typical thickness of the bonded lubricant layer is of about 4 to 8 Angstroms, and that of the free lubricant layer is of about 12 to 16 Angstroms.
In the hard disk drives with thin-film heads of the prior art, the typical fly height of the sliders is of about 2 micro-inch (about 500 Angstroms). However, in the present hard disk drives with magneto-resistive (MR) heads, the fly height of the slider decreases to about 1 micro-inch (about 250 Angstroms). Hence, the pressure between the slider and the disk surface becomes sub-ambient more to do with the vacuum pressure air bearing design. Consequently, lubricant on the disk surface is easily absorbed to the slider, and this will increase the flying stiction of the magnetic head assembly.
U.S. Pat. Nos. 4,960,609, 4,642,246 and 5,030,478 respectively disclose inert gas plasma, heating and UV radiation methods for forming a lubricant layer on a disk. With the above methods of the prior art, the CSS test at high temperature (35 degrees C) and humidity (80% RH) of hard disk drives can be passed since the thickness of the free lubricant layer on the data zone according to the prior art is decreased. Hence, the flying stiction of the magnetic head assembly on the data zone is obviously reduced. Unfortunately, the thickness of the free layer on the landing zone is also decreased. Thismay induce wear of the disk surface. In order to solve the above problem, a magnetic disk with zoned lubricant thickness is proposed by the U.S. Pat. No. 5,650,900.